Try using the insert menu from the top
INSERT
MANUFACTURING GEOMETRY
MILL VOLUME
then insert a extrude
INSERT
EXTRUDE
If that doesn't work attach your file so we can see if there is something else going on.
Try using the insert menu from the top
INSERT
MANUFACTURING GEOMETRY
MILL VOLUME
then insert a extrude
INSERT
EXTRUDE
If that doesn't work attach your file so we can see if there is something else going on.